This is a request for an NIMH Scientist Development Award for Clinicians (K-20) entitled "Developing Probes of Cortico-Striatal Circuitry." The candidate's interest is in the neuroscience of neuropsychiatric disorders involving the basal ganglia, particularly obsessive-compulsive disorder (OCD) and Tourette's disorder (TS). Cortico-striatal circuits have been implicated in the pathophysiology of OCD and TS. Although converging data suggest that separate cortico-striatal circuits are arranged in a parallel, segregated fashion, and that different cortico-striatal circuits mediate the symptoms of the two disorders, the capacity to empirically test such hypotheses has been limited. The candidate proposes to devise and implement specific activation paradigms to probe discrete parallel cortico-striatal circuits individually, using positron emission tomography (PET) to study adult subjects. In addition to activation studies to determine the mediating neuroanatomy of TS and OCD, receptor characterization techniques will be employed to explore possible neurochemical abnormalities within the striatum. Such a multifaceted approach to the study of cortico-striatal circuits promises to yield important information about OCD, TS, and the physiological functions of cortico-striatal systems.